The present invention is directed to cooling granular or the like materials using ambient air, and more particularly to an apparatus and method for cooling a granular material, such as a phosphate fertilizer.
In fertilizer production, it is important that the freshly made fertilizer, such as diammonium phosphate (DAP), monoammoniumphosphate (MAP), etc, be cooled properly for an effective evaporation of the residual water from the fertilizer granules. Although the fertilizer coming out from the end of a production cycle is generally at a temperature of about 195.degree. to 210.degree. F. and appears dry, there is residual water inside each individual granule. Further, while the process of water migrating from inside a granule to its outside skin is continuous and ongoing, if the internal residual water does not have a way to escape, or if insufficient evaporation takes place, the apparently dry granules remain wet. If the fertilizer in this wet condition is allowed to be stored, the granules tend to stick together in a pile causing the fertilizer caking problem. Typically, freshly made fertilizer is stored in buildings, rail cars, or barges for shipping and handling, where the caking takes place.
In fertilizer industry, the caking problem could be severe in that it is not uncommon to break loose the piles of fertilizer using dynamite. It is known to have taken days, instead of minutes, to unload railcars and trucks due to the fertilizer caking. The caking of fertilizer not only is undesirable from the quality standpoint, but leads to unnecessary expenses that must be incurred under these circumstances.
In order to solve the caking problem, many dry product coolers have been designed. The most common cooler in fertilizer plants is the Countercurrent Rotary Drum Cooler. The other less commonly used devices include Fluid Bed Cooler, Heat Exchanger Fluidized Bed, and the Bulk Flow Plate Heat Exchanger. These coolers are huge and heavy, costly to build and install and to maintain and operate. A complete conventional cooling system is known to cost several million dollars.
U.S. Pat. Nos. 265,552; 764,805; 2,435,927; 2,458,357; 4,126,946; 4,187,988; and 4,205,792, are directed to various drying, cooling and distributing devices.
In view of the problems associated with conventional techniques, there is a need in the industry for an efficient method and device for preventing fertilizer caking which is simple in design, economical, easy to operate and inexpensive to maintain.